The invention relates to a connection structure for an automatic transmission.
Automatic transmissions often use many clutch (and brake) drums in which an inner peripheral face of a clutch (and/or brake) drum member formed from a press-molded cylindrical member is outwardly engaged to a base member formed from a cylindrical member. The engaging faces are then welded by an electron beam or the like from the outside (see, for example, Japanese Patent Application Publication No. JP-A-61-48616).
In addition, a planetary gear is disposed adjacent to the clutch drum, and a connection structure is used so as to integrally fix a predetermined element of the planetary gear, such as a ring gear, to the clutch drum (see, for example, published patent application, Japanese translation of PCT international application No. 2005-527744).
The above connection structure is generally a welded structure. As such, precision may be compromised in predetermined rotation elements such as the ring gear due to warping or the like caused by the effects of heat during welding. Furthermore, other problems such as gear noise and less gear durability can occur.
Furthermore, the clutch (or brake) drum member is in spline engagement with a plurality of friction plates and has a predetermined length in the axial direction. A large bending moment (wrenching force) acts on the engaging faces in accordance with the engagement of friction plates and the like. A bending moment thus acts on the welded portion in a concentrated manner. As a result, the structure of the clutch (or brake) drum member has disadvantages in terms of strength with respect to the welded portion and a portion thereof affected by heat.
In addition, formed on an inner peripheral portion of the drum member is a boss-shaped collar portion extending toward the axial direction. The collar portion is often pressed into an outer peripheral face of the base member and an edge portion thereof may be welded. However, this involves a significant amount of surface area for the press fitting and is accompanied by a corresponding increase in the pressing load.
Moreover, the drum member may be integrally fixed to the base member as follows to reduce such a load and simplify assembly. An engaging face of the base member has a stepped structure in which only an edge portion thereof is dimensioned for press fitting, whereas other portions are set to have a slight minor diameter. Only an edge portion of the collar portion is pressed into and positioned in the base member. In such a state, the entire periphery of the edges of the collar portion and the base member are welded.
With the engaging face formed in such a stepped structure, a narrow clearance is created between an outer peripheral face of a minor diameter portion of the base member and an inner peripheral face of the collar portion. Thus, if a foreign substance were to penetrate the clearance during production, it would be impossible to eliminate the foreign substance by a washing process or the like due to the narrowness of the clearance. The contaminated connection member is subsequently assembled to an automatic transmission as a friction engagement device, after which the foreign substance may escape from the clearance during operation of the automatic transmission. The foreign substance could then cause a problem in the automatic transmission.